Non-contact wet wafer holder

ABSTRACT

The present invention relates to a load cup configured to speed up substrate transferring to and from a carrier head and to reduce corrosion during the transferring. One embodiment of the present invention provides a non-contact substrate holder comprising a pedestal having a top surface configured to support a substrate, and at least one injection port configured to eject a high velocity liquid stream on the top surface of the pedestal, wherein the liquid stream in configured to secure the substrate on the pedestal without the substrate contacting the top surface of the pedestal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to an apparatus and a method for transferring a substrate.

2. Description of the Related Art

Sub-micron multi-level metallization is one of the key technologies for the next generation of ultra large-scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, trenches and other features.

Planarization is generally performed using Chemical Mechanical Polishing (CMP) and/or Electro-Chemical Mechanical Deposition (ECMP). A planarization method typically requires that a substrate be mounted in a carrier head, with the surface to be polished exposed. The substrate supported by the carrier head is then placed against a rotating polishing pad. The carrier head holding the substrate may also rotate, to provide additional motion between the substrate and the polishing pad surface. A polishing solution is usually supplied to the rotating polishing surface to assist the planarization process.

During the planarization process, the substrate is generally secured on the carrier head from the backside of the substrate, for example by forming vacuum cups between a membrane on the carrier head and the backside of the substrate. Prior to or after the planarization process, a load cup is generally used for substrate transferring to and from a carrier head.

In the state of the art load cup may have a substrate supporting means, for example, support fingers, configured to hold a substrate and transfer the substrate to and from the carrier head. When unloading a substrate from a carrier head, the membrane is usually inflated to release the vacuum cups between the membrane and the backside of the substrate. The substrate will then fall off the carrier head to a load cup underneath under the effect of gravity. FIG. 1 schematically illustrates a substrate holder used in the state of the art load cup. A carrier head 10 having a membrane 11 configured to secure a substrate 12 thereon. The membrane 11 is inflated so that the substrate 12 is no longer “sucked” to the carrier head 10. A substrate holder 15 having a plurality of support fingers 14 is positioned underneath the carrier head 10 to catch the substrate 12 once the substrate 12 falls off the carrier head 10 under the effect of gravity. During this transferring process, a processed surface 13 of the substrate 12 is exposed to air or other process environment. The processed surface 13 is generally wet from polishing solutions on polishing stations. Structures, such as copper structures, easily corroded when exposing to air in a wet condition.

The state of the art load cup has several limitations. First, the time takes to unload a substrate from a carrier head is relatively long and unpredictable since it passively waits for gravity to take effect. Second, a substrate to be unloaded is generally wet and exposed to atmosphere during unloading resulting in corrosion on the processed surface.

Therefore, there is a need for apparatus and method to transfer a substrate at an increased and predictable rate and with decreased corrosion.

SUMMARY OF THE INVENTION

The present invention generally relates to a substrate transferring system. Particularly, the present invention relates to a load cup configured to speed up substrate transferring to and from a carrier head and to reduce corrosion during the transferring.

One embodiment of the present invention provides a non-contact substrate holder comprising a pedestal having a top surface configured to support a substrate, and at least one injection port configured to eject a high velocity liquid stream on the top surface of the pedestal, wherein the liquid stream in configured to secure the substrate on the pedestal without the substrate contacting the top surface of the pedestal.

Another embodiment of the present invention relates to a method for transferring a substrate comprising holding the substrate using a first substrate holder, flowing a liquid stream on a support surface of a second substrate holder, contacting a surface of the substrate with the liquid stream formed on the support surface of the second substrate holder, releasing the substrate from the first substrate holder, and pulling the substrate from the first substrate holder using the liquid stream without letting the substrate contacting the second substrate holder.

Yet another embodiment of the present invention relates to a method for chucking a substrate comprising flowing a liquid stream on a support surface of a pedestal, wherein the liquid stream forms a liquid bed on the support surface of the pedestal, and positioning a surface of the substrate on the liquid bed, wherein the surface of the substrate is substantially parallel to the liquid stream, and the surface of the substrate does not contact the support surface of the pedestal.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 (prior art) schematically illustrates a substrate holder used in the state of the art load cup.

FIG. 2 schematically illustrates a planarization system in accordance with one embodiment of the present invention.

FIG. 3 schematically illustrates a non-contact substrate holder in accordance with one embodiment of the present invention.

FIGS. 4A-4D schematically illustrate a substrate unloading method in accordance with one embodiment of the present invention.

FIGS. 5A-5C schematically illustrate a substrate loading method in accordance with one embodiment of the present invention.

FIG. 6A schematically illustrates a sectional side view of a substrate holder in accordance with one embodiment of the present invention.

FIG. 6B schematically illustrates a top view of the substrate holder of FIG. 6A.

DETAILED DESCRIPTION

The present invention generally relates to an apparatus and a method for transferring a substrate, particularly relates to substrate transferring between a load cup and a carrier head in a chemical mechanical polishing (CMP) system or electrochemical mechanical polishing (ECMP) system.

FIG. 2 illustrates a partial sectional view of a polishing system 100. The polishing system 100 comprises a polishing station 102, a carrier head 104 and a load cup 110. The polishing station 102 comprises a rotatable platen 106 having a polishing material 116 disposed thereon. The carrier head 104 is supported above the polishing station 102 coupled to a base 126 by a transfer mechanism 118. The transfer mechanism 118 is adapted to position the carrier head 104 selectively over the polishing material 116 or over the load cup 110 (shown in dotted lines). The carrier head 104 comprises a membrane 150 configured to hold a substrate 146 thereon. A detailed description of the carrier head 104 may be found in U.S. Pat. No. 6,183,354, entitled “Carrier Head with a Flexible Membrane for a Chemical Mechanical Polishing”, and U.S. patent application Ser. No. 11/054,128 filed on Feb. 8, 2005 now U.S. Pat. No. 7,001,257, entitled “Multi-chamber Carrier Head with a Flexible Membrane”, which are herein incorporated as reference.

The load cup 110 generally includes a pedestal assembly 128 configured to support a substrate thereon without contacting the substrate. The pedestal assembly 128 is supported by a shaft 136 which is coupled to an actuator 133. When transferring a substrate between the load cup 110 and the carrier head 104, the carrier head 104 is generally rotated to above the load cup 110, as shown in the dotted lines. The membrane 150 may be inflated to release the substrate 150 which is then grabbed by the load cup 104.

In one embodiment of the present invention, the pedestal assembly 128 is a non-contact substrate holder which uses pulling force from a high velocity liquid stream to chuck a substrate thereon.

FIG. 3 schematically illustrates a non-contact substrate holder 200 in accordance with one embodiment of the present invention. The non-contact substrate holder 200 is configured to secure a substrate using a liquid bed formed from a liquid stream. The non-contact substrate holder 200 may be used as the pedestal assembly 128 of the polishing system 100 of FIG. 2.

The non-contact substrate holder 200 comprises a pedestal 201 having a top surface 203. An injection port 209 is formed on the pedestal 201 near a center of the pedestal 201. The injection port 209 is in fluid communication with a channel 204 formed in the pedestal 201. The channel 204 may be connected to a fluid source 210 configured to pump a liquid at a high velocity onto the top surface 203 through the injection port 209. In one embodiment, a fluid may be pumped out of the injection port 209 at a flow rate between about 500 cc/min and about 2000 cc/min. In one embodiment, the flow rate from the injection port 209 may be about 1000 cc/min. In one embodiment, an insert 202 may be disposed in the channel 204. The insert 202 is configured to direct the liquid flow from the injection port 209 to be substantially parallel to the top surface 203 of the pedestal 201 such that a liquid bed may be formed on the top surface 203.

During operation, the fluid source 210 pumps a liquid to the channel 204. The liquid forms a liquid stream 205 on the top surface 203. In one embodiment, the liquid stream 205 with high velocity flows from the center of the top surface 203 toward a periphery of the top surface 203 and forms a liquid bed that covers the top surface 203. The flow rate of the liquid stream 205 and the thickness of the liquid bed may be controlled within a range that a substrate 208 may be chucked above the pedestal 201. In one embodiment, the thickness of the liquid bed may be controlled by controlling the flow rate from the injection port 209.

The substrate 208 is positioned on top of the liquid stream 205 so that a surface 211 of the substrate 208 is in contact with the liquid stream 205. In one embodiment, the surface 211 of the substrate 208 is sealed by the liquid stream 205. It has been proven that when the surface 211 is in contact with the liquid stream 205, the liquid stream 205 “pull” the substrate 208 so that the substrate 208 is chucked on the liquid bed formed by the liquid stream 205, yet not in contact with the top surface 203 of the pedestal 201.

It is shown that a high velocity liquid stream, such as the liquid stream 205 from the injection port 209, creates a pull force that increases as a substrate approaches a supporting surface, such as the top surface 203. At the same time, the liquid stream, with high pressure, generates a push force which also increases at the substrate gets closer to the support surface. The push and pull forces act on different regions around the injection port (thus on different regions of the substrate) and balance out with each other. Thus, when positioned above a supporting surface covered by a high velocity liquid stream from an injection port, a substrate is constantly pulled towards the support surface, but never contacts the support surface.

Curve 220 of FIG. 3 schematically illustrates distribution of a force applied to the substrate 208 by the liquid stream 205. The upward direction indicates a push force and the downward direction indicates a pulling force. The distribution of the force is in accordance with computer simulation and bench measurements. As illustrated by curve 220, the substrate 208 is pulled right above the injection port 209, pushed at regions immediately near the injection port 209, pulled at regions extending radially outwards from the pushed region, and then pushed again outside the pulled region.

One explanation of the pull force on the substrate 208 from the liquid stream 205 is the Bernoulli Principle: for an ideal liquid, with no work being performed, an increase in velocity occurs with decrease in pressure or gravitational energy. An alternative explanation of the pull force may be the momentum principle: pressure drops as high momentum fluid expands over larger volume.

Even thought, the exact explanation of the pulling force may be controversial, the physical phenomenon is unquestionable. In one embodiment, a liquid stream for one injection port may provide a pulling force of about 20 lb.

In one embodiment, the non-contact substrate holder 200 may comprise one or more sensors configured to detect the presence of a substrate. In one embodiment, a sensor 206 a is disposed in the pedestal 201 and configured to measure a pressure on the top surface 203. The sensor 206 a may be disposed in a pulling region of an injection port, such as the injection port 209. In another embodiment, a sensor 206 b may be disposed near the center of the injection port and configured to measure a pressure on the top surface 203. When a substrate is not present, measurement from the sensor 206 a or 206 b is approximately the environment pressure, for example, the atmosphere pressure. When a substrate is chucked on the non-contact substrate holder 200, measurement of the sensor 206 a or 206 b reflects a negative pressure because a pulling force is applied to the substrate and the top surface 203. In one embodiment, the sensor 206 is a pressure transducer.

Accordingly, a sensor may be disposed in push region of an injection port to measure the positive pressure caused by presence of a substrate.

The sensor 206 a or 206 b may be further connected to a controller 207, which may be informed by the sensor 206 a or 206 b of the presence or non presence of a substrate.

The liquid used in the non-contact substrate holder 200 may be any liquid solution suitable for contacting a substrate surface. In one embodiment, the liquid is deionized water (DI water). In another embodiment, the liquid may be a cleaning solution.

FIGS. 4A-4D schematically illustrate a substrate unloading method in accordance with one embodiment of the present invention. FIGS. 4A-4D schematically illustrate using the non-contact substrate holder 200 to unload a substrate 208 mounted on a carrier head 300.

The carrier head 300 comprises a body 301 having a supporting surface 302. A plurality of dimples 303 are formed on the supporting surface 302. A membrane 304 configured to secure a substrate thereon is disposed around the supporting surface 302. The membrane 304 may be inflated and deflated. When the membrane 304 is deflated, a plurality of vacuum cups 305 may be formed between the substrate 208 and the membrane 304 so that the substrate 208 is “sucked” on the membrane 304. When the membrane 304 is inflated, the vacuum cups 305 are released, and the substrate 208 is no longer secured on the membrane 304.

Generally, unloading a substrate from a carrier head, such as the carrier head 300, includes releasing a securing force, in this case the vacuum suction force from the membrane 304. After the vacuum force is released, a substrate once secured to the membrane 304 is left to fall off under the effect of gravity. However, it takes a relatively long time for a substrate to fall off the membrane and the time may vary from substrate to substrate. The relative long time for a substrate to fall not only reduces throughput, but also increases the substrate's chances of exposing to corrosion and contamination. Variation of falling time also introduce inconsistency to from substrate to substrate.

Embodiments of the present invention provide a method for actively unload a substrate from a carrier head to increase unloading speed and provide consistency among substrates.

As shown in FIG. 4A, the carrier head 300 with the substrate 208 secured on the membrane 304 approaching the non-contact substrate holder 200. A liquid bed is formed on the top surface 203 of the pedestal 201 by the liquid stream 205 ejected from the injection port 209.

In FIG. 4B, the carrier head 300 and the non-contact substrate holder 200 move towards each other, this may be achieved by lowering the carrier head 300 and/or raising the non-contact substrate holder 200. In one embodiment, the carrier head 300 and the non-contact substrate holder 200 may be positioned such that a gap 307 remains between the substrate 208 retained by the carrier head 300 and the liquid stream 205 on the non-contact substrate holder 200. In one embodiment, the gap 307 may be about 6 mm.

In FIG. 4C, the carrier head 300 and the non-contact substrate holder 200 remain still relative to one another. The membrane 304 may be inflated and the substrate 208 is pushed towards the liquid stream 205 and is eventually “grabbed” from the membrane 304 by the pulling force from the liquid stream 205. In one embodiment, the sensor 206 a or 206 b may be used to confirm the chucking of the substrate 208.

In FIG. 4D, the carrier head 300 and the non-contact substrate holder 200 pull away from each other and the substrate 208 is unloaded on the non-contact substrate holder 208.

In one embodiment, the steps in FIGS. 4B and 4C may be combined. The carrier head 300 and the non-contact substrate holder 200 move relative to each other such that the substrate 208 is in contact with the liquid stream 205 but not in contact with the top surface 203 of the pedestal. The membrane 304 may be inflated and the substrate is grabbed from the membrane 304 by the pulling force from the liquid stream 205.

If the carrier head 300 is used in a polishing process, the surface 211 is generally the device side of the substrate where devices are formed. The surface 211 is usually semi-wet from the processes performed in a polishing system and venerable to corrosion when exposed to atmosphere. The unloading process described above limits the time the semi-wet surface 211 exposed to atmosphere, therefore, reduces corrosion.

FIGS. 5A-5C schematically illustrate a substrate loading method in accordance with one embodiment of the present invention. FIGS. 5A-5C schematically illustrate loading a substrate onto a carrier head using a non-contact substrate holder of the present invention.

FIG. 5A shows, prior to loading the substrate 208 onto the carrier head 300, the substrate 208 is chucked on the non-contact substrate holder 200. The surface 211, i.e. the device side, is in contact with the liquid stream 205 and sealed therein.

In FIG. 5B, the carrier head 300 and the non-contact substrate holder 200 move towards each other, this may be achieved by lowering the carrier head 300 and/or raising the non-contact substrate holder 200. The carrier head 300 and the non-contact substrate holder 200 are positioned in a distance such that a back side 212 of the substrate 208 is in contact with the membrane 304. In one embodiment, the membrane 304 may be first inflated to get rid of air bubbles between the membrane 304 and the back side 212 of the substrate 208. The membrane 304 is then deflated to create vacuum cups between the membrane 304 and the back side 212 of the substrate 208.

In FIG. 5C, the liquid stream 205 is stopped and the substrate 208 is dechucked. The substrate 208 is now loaded on the carrier head 300. The carrier head 300 and the non-contact substrate holder 200 may pull away from each other.

FIG. 6A schematically illustrates a sectional side view of a substrate holder 400 in accordance with one embodiment of the present invention. FIG. 6B schematically illustrates a top view of the substrate holder 400 of FIG. 6A.

The substrate holder 400 comprises a pedestal 401 having a supporting surface 403 configured to retain a liquid bed thereon. A plurality of injection ports 404 are formed on the pedestal 401. Each of the plurality of injection ports 404 is configured to flow a high velocity liquid stream onto the supporting surface 403 to form the liquid bed for supporting a substrate 208 thereon.

In one embodiment, a retaining lip 409 may be formed on a periphery of the pedestal 401. The retaining lip 409 may be used to align the substrate radially.

Referring to FIG. 6B, the plurality of injection ports 404 may be evenly distributed on the support surface 403 such that pulling forces generated from the plurality of injection ports 404 may be distributed evenly on a substrate to be chucked thereon.

In one embodiment, the injection port 404 may comprise an insert 402 configured to direct a liquid stream from the injection port 404. A fluid supply channel 405 formed in the pedestal 401. The fluid supply channel 405 may be in fluid communication with a liquid source. In one embodiment, a sensor 406 may be present in the insert 406. The sensor 406 may be configured to measure a negative pressure caused by the presence of a substrate.

Even though a planarization process is described with the non-contact substrate holder of the present invention, a person skilled in the art can apply the non-contact substrate holder for holding and transferring substrates in any suitable processes, such as wet cleaning, electroplating, and electroless plating.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A non-contact substrate holder, comprising: a pedestal having a top surface configured to support a substrate; and an injection port disposed within the top surface of the pedestal and configured to eject a high velocity liquid stream onto the top surface of the pedestal and to direct the liquid stream substantially parallel to the top surface of the pedestal, wherein the liquid stream is configured to secure the substrate to the pedestal without contact between the substrate and the top surface of the pedestal.
 2. The non-contact substrate holder of claim 1, wherein the injection port comprises an insert disposed within a fluid channel.
 3. The non-contact substrate holder of claim 1, further comprising a sensor configured to detect presence of the substrate.
 4. The non-contact substrate holder of claim 3, wherein the sensor is a pressure transducer.
 5. The non-contact substrate holder of claim 3, wherein the sensor is positioned within the injection port.
 6. The non-contact substrate holder of claim 1, further comprising a plurality of injection ports disposed within the top surface.
 7. A method for transferring a substrate, comprising: holding the substrate using a first substrate holder; flowing a liquid stream onto a support surface of a second substrate holder; contacting a surface of the substrate with the liquid stream flowed onto the support surface of the second substrate holder; releasing the substrate from the first substrate holder; and attracting the substrate to the second substrate holder via the liquid stream, wherein the substrate does not contact the support surface of the second substrate holder.
 8. The method of claim 7, wherein flowing the liquid stream comprises flowing deionized water.
 9. The method of claim 7, wherein flowing the liquid stream comprises flowing a cleansing solution.
 10. The method of claim 7, further comprising detecting presence of the substrate using a pressure sensor disposed on the support surface of the second substrate holder.
 11. The method of claim 7, wherein flowing the liquid stream comprises injecting high velocity liquid from an injection port disposed within the support surface of the second substrate holder.
 12. The method of claim 7, wherein flowing the liquid stream comprises injecting a liquid from a plurality of injection ports disposed within the support surface of the second substrate holder.
 13. The method of claim 7, wherein the first substrate holder is a carrier head used in a polishing system.
 14. The method of claim 7, wherein the first substrate holder is a robot configured to transfer substrates.
 15. A method for chucking a substrate, comprising: flowing a liquid stream onto a support surface of a pedestal, wherein the liquid stream forms a liquid bed on the support surface of the pedestal; and placing the substrate on the liquid bed, wherein a surface of the substrate is substantially parallel to the flow of the liquid stream, and the surface of the substrate does not contact the support surface of the pedestal.
 16. The method of claim 15, wherein the liquid stream flows at a high velocity.
 17. The method of claim 15, wherein the liquid stream comprises deionized water.
 18. The method of claim 15, wherein the liquid stream comprises a cleansing solution.
 19. The method of claim 15, wherein flowing the liquid stream comprises injecting a high velocity liquid from an injection port disposed within the support surface of the pedestal.
 20. The method of claim 15, further comprising sensing the presence of the substrate using a pressure sensor disposed on the support surface of the pedestal. 